Display screen or portion thereof with a graphical user interface



FIG. 1 is a face view of a display screen or portion thereof with a graphical user interface, showing my new design and illustrating a first embodiment of the design; and,

FIG. 2 is a face view of a display screen or portion thereof with a graphical user interface, illustrating a second embodiment of the design.

The difference in shading indicates a contrast of appearance and does not depict any particular color, texture, or material.

The outermost double broken lines represent the article and form no part of the claimed design. The broken lines within the display screen show portions of the graphical user interface and forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 